【作者】 杨超；

【导师】 王文魁； 刘日平； 孙力玲；

【作者基本信息】 燕山大学 ， 材料学， 2006， 博士

【摘要】 本论文以Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5合金体系为研究对象,首先研究了重力场驱动其合金熔体中不同密度和尺寸的粒子的输运行为对合金熔体玻璃形成能力的影响,以制备成分均匀的大块金属玻璃材料。通过高速撞击实验,研究大块金属玻璃的损伤特征和断裂机理,以及冲击波淬火作用下大块金属玻璃的形成机制。利用多种实验手段,对比研究水淬法和冲击波淬火法制备的大块金属玻璃的短程结构、热稳定性、晶化动力学和相演化过程。通过这些研究,揭示冲击波效应对大块金属玻璃结构和稳定性的影响。本论文利用二级轻气炮加速弹丸进行的高速撞击实验,采用扫描电子显微镜研究了Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5大块金属玻璃在平面冲击波和球面波作用下的损伤特征和断裂机制。利用二级轻气炮驱动平面飞片产生的高温、高压,研究了冲击波淬火条件下Zr41Ti14Cu12.5Ni10Be22.5合金熔体的玻璃形成能力及玻璃形成的物理机制。运用超声测量和密度测量,对比研究了水淬法和冲击波淬火法制备的Zr41Ti14Cu12.5Ni10Be22.5大块金属玻璃的热弹性参数;利用差示扫描量热分析技术,研究了这两种大块金属玻璃的玻璃转变和晶化动力学;利用同步辐射X射线,研究了这两种大块金属玻璃的短程结构;运用高温原位X射线,研究了连续加热条件下这两种大块金属玻璃的晶化过程;利用高温高压同步辐射X射线,研究了压力对这两种大块金属玻璃的晶化温度和相演化过程的影响。研究结果表明,ZrTiCuNiBe淬态合金棒中沿着轴线从底端到顶端铍原子出现的成分梯度分布现象,是由重力场驱动合金熔体中富铍粒子的斯托克斯运动造成的,它极大地影响合金熔体的玻璃形成能力;平面飞片高速撞击后,被撞击表面形成了径向裂纹,绝热剪切带/裂纹内出现了由高应变速率变形导致的严重熔化现象（“类似于液滴坑”）;在压缩应力作用下,大块金属玻璃的断裂平面与冲击方向的夹角为35°;球形弹丸高速撞击后,大块金属玻璃靶内部出现了各种断裂裂纹和均匀分布的微孔洞;无论是在压缩应力还是在拉伸应力作用下,大块金属玻璃的断裂都是微孔洞的形核、长大合并、以及连接的过程,微孔洞的形成起源于大块金属玻璃内多余自由体积的释放和合并;相对于水淬法制备的大块金属玻璃,冲击波淬火法制备的大块金属玻璃具有更高的玻璃转变温度、晶化温度、晶化峰值温度和热稳定性,以及更大的声速和更小的密度;冲击波淬火和水淬大块金属玻璃径向分布函数的第一更多还原

【Abstract】 In order to prepare homogeneous bulk metallic glass （BMG）, gravity-drivenberyllium transport in ZrTiCuNiBe melt and its influence on glass formation isinvestigated by a long time holding of metallic melts at above its liquidus temperature.The purpose of this dissertation is that investigating damage characteristics and fracturemechanism of Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5BMG impacted by high-speed projectiles,formation mechanism of the BMG by shock-wave quenching, and short-range orderstructure and crystallization kinetics and phase evolution using many experimental ways.Furthermore, another purpose of the dissertation is to reveal effects of shock wave onBMG.Damage characteristics and fracture mechanism of the BMG under planar shockwave and spherical wave are studied by scanning electron microscopy after impact ofhigh-speed projectiles fired by a two-stage light gas gun. Glass forming ability andformation mechanism of the BMG is investigated by shock-wave quenching of hightemperature and high pressure caused by high-speed impact. Thermal-elasticity propertiesof BMGs prepared by water quenching and shock-wave quenching are investigated byultrasonic and density measurements. Glass transition and crystallization kinetics,short-range order structure and crystallization process of the two BMGs are investigatedby differential scanning calorimetry, synchrotron radiation X-ray diffraction and hightemperature in situ X-ray diffraction, respectively. Pressure effects on crystallizationprocess and crystallization temperature of the two BMGs under high temperature and highpressure are also studied by in situ synchrotron radiation X-ray diffraction.The results show that the upper part of a quenched Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk alloyrod contains more beryllium atoms and is amorphous. But the lower part with lessberyllium atoms contains crystalline phases. The composition gradient is possibly due tothe gravity-driven transport of Be-rich clusters and unmelted tiny solid pieces in the alloymelt. Under the impact of planar flyer, radial symmetric cracks form on the shockedsurface of the Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 BMG target. Shear cracks/bands about 35o to theshocking direction are found in the layer subjacent to the shocked surface. Evidences ofcrystallization and melting （liquid droplet-like pit） due to high strain rate deformation arealso observed inside adiabatic shear cracks/bands. Under the impact of sphericalprojectiles, crater profiles and lamination cracks are presented in addition to the adiabaticshear cracks/bands. Under compressive or tensile stress, cracking of the BMG follows aprocess of nucleation, growth, and coalescence of micro-voids in shear bands, which werepossibly initiated by release and coalescence of excess free volumes. Compared withwater-quenched Zr41Ti14Cu12.5Ni10Be22.5 BMG, shock-wave-quenched BMG exhibitshigher glass transition temperature, crystallization temperature, crystallization peaktemperature, thermal stability, and bigger acoustic velocities and lower density.Shock-wave-quenched BMG has higher coordination numbers in the range of r 2.4-5.6? and lower numbers in the range of r ⁵.6-9.5 ? than those for a water-quenched one.The first coordination number, N=14.4 and 14.0, is estimated from a distance of 2.1-3.7 ?for shock-wave-quenched sample and water-quenched one, respectively. Undercontinuous heating conditions, shock-wave-quenched BMG possesses different phasesand different precipitation sequences form those for water-quenched and shock wavetreated ones, respectively. The differences in crystallization are probably attributed todifferent atomic configurations between the three BMGs treated by different ways. Atdifferent pressures, the BMGs prepared by shock-wave quenching and water quenchingexhibit the same primarily precipitated phase, yet the following crystallization sequencesare different. The onset temperature of crystallization is found to increase with pressurefor the two BMGs, but with a sudden drop at about 5.6 and 6.0 GPa for water-quenchedBMG and shock-wave-quenched one respectively, which correspond to differentcrystallization sequence at about 5.6 and 6.0 GPa in comparison with those at otherpressures for water-quenched BMG and shock-wave-quenched ones. These may beattributed to that the BMGs possess different atomic configurations at different pressures.更多还原